Timing in silicon detectors for a Compton PET camera

In the scope of construction of a PET apparatus based on detection of Compton scattering in silicon (Compton camera), the timing properties of silicon pad detectors and single and double-sided microstrip detectors are studied. Timing in pad detectors is also studied for 140.5 keV /sup 99m/Tc and 364.5 keV /sup 131/I gamma rays in view of a SPECT application. Compton scattering and energy loss of the Compton electron in silicon detector are simulated using the GEANT package. The electric field in the detector is calculated numerically for a fully depleted detector in the abrupt junction approximation, taking into account the geometry and varying the reverse voltage. Signal formation is studied using Ramo's theorem and pulse shaping properties of the trigger circuit. The time-walk cut is seen to be directly corresponding to a deposited-energy cut. At a 10 keV threshold in 1 mm thick detectors, 10 ns timing windows are shown to cut a significant portion of events, degrading efficiency or limiting the angular range in a prohibitive way.